In situ observation of defects in hydroxyapatite up to 1200°C by ultraviolet Raman spectroscopy

Raman spectra of hydroxyapatite have been successfully obtained at temperatures up to 1200°C for the first time by using a new system of ultraviolet (UV) Raman spectroscopy. With increasing temperature, the intensity of a band ascribed to the stretching vibration of the OH ion continuously decreased. The total intensity of bands in the wavenumber range of 3300–3800 cm−1 did not change significantly up to about 800°C, whereas they decreased at temperatures higher than about 800°C. This result is interpreted as producing oxy-hydroxyapatite due to dehydration of hydroxyapatite over 800°C. The withdrawal of water is accompanied by the creation of defects. This consideration is strongly supported by results of thermodynamic calculations and the line width of the Raman band.